Channel Flow Simulation Using Converge Science

CHANNEL FLOW SIMULATION USING CONVERGE SCIENCE

Objective :

To Simulate the air flow through a channel by using Converge CFD for 3 different Mesh Sizes and comparing the results .

Mesh Sizes to Compare :

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

Introduction:

In order to set up a Simulation in Converge CFD we have to follow steps:

1. Pre – Processing
2. Running the Simulation
3. Post Processing

PRE – PROCESSING:

1. Geometry: We create geometry of the Channel followed by checking the geometry if it’s clean by diagnosing.

Follow : Geometry tab -> Create->Shape->Box>Input Dimensions -> Create

Size in Meters (dx,dy,dz) = 0.1, 0.01, 0.01

Centre in Meters (dx,dy,dz)=0.05, 0.00, 0.00

2. Diagnosis : To check if there is some errors regarding the geometry .

Follow : Diagnosis Tab->Find

The Geometry as diagnosed is clean as indicated by check points .

Select the normal and transform the normal direction inside (Sink form) as the flow is within the channel

3. Creating Boundary : It includes Inlet , Outlet , Wall , Pressure Boundary conditions.

Follow : Geometry tab -> Boundary->Flag->Create Multiple Boundaries ->Ok.

For the Channel we need to set up 5 Boundary Conditions :

Inlet : Where the flow will enter, we have to select the 2 Triangles to setup the Initial BC.

Outlet: Where the flow shall exit .

Top and Bottom Walls : The Walls of the Channel.

Front 2D

Back 2D

4. Case Setup :

We have to setup the case where we have to define certain parameters for our Channel Flow

• Application: Since our case is of a normal form , Follow : General Flow-> Done.
• Materials : Select Gas Simulations & Species , in Species add Nitrogen & Oxygen.

Global Transport Parameters as default .

• Simulation Parameters :

Run Parameters: Solver – Pressure Based Steady Solver

Simulation Mode-Full Hydrodynamic

Gas Flow Solver – Compressible

Simulation Time Parameter : As Shown

Solver Parameter : Default

• Boundary Conditions : In this particular section which is very crucial , we have to assign the Boundary type to each of our different Boundary that we have created , in our case 5.

Inlet : Boundary Type – Inflow

Pressure Boundary Conditions : Specified Value-100001.0 Pa

Species Boundary Condition : O2 - 0.23 , N2 – 0.77

Outlet: Boundary Type – Outflow

Pressure Boundary Conditions : Specified Value-100000.0 Pa

Species Boundary Condition : O2 - 0.23 , N2 – 0.77

Front & Top Wall : Boundary Type – Wall

Surface Movement – No Slip

Front 2D: TWO_D

Back 2D : TWO_D

• Initial Conditions and Events : Under Regions and Initialization we shall choose Air and select species and change the composition as O2-0.77 & N2-0.23 and rename region name as Volumetric Region User Defined.

And in the Boundary Conditions Head,we will assign regions to our defined Boundary Conditions

• Physical Models : We shall uncheck all the Turbulence Check Points as our flow is laminar .

• Grid Control: In the Grid Control under Base Grid Size we shall assign the values as depicted for our

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

• Output / Post Processing : We set parameters for Post processing

Post Variable Selection : Uncheck all Turbulent related check points and under Species add O2 and N2.

Output Files : Select the Time interval to write output Time Interval for writing 3D Output Data Files 100 as we have set 15000 as our time total cycles.

Case Setup is Completed :

• Export Files: Export the files to the Saved case Directory which shall be used for Simulation .

We are completed with our Pre – Processing and exported files for Simulation .

RUNNING THE SIMULATION:

To Simulate we have to run the EXECUTER which is CYGWIN64.

We navigate to the saved directory and run the simulation using the commands as depicted.

We save the results obtained by the Simulation in logfile_1.

To view the Total Simulation time :

Then we Post Convert these files in order to export it in the form executable in ParaView to visualize the output. In our Case we convert post.out files using ENSIGHT converter into .case file .

POST PROCESSING:

The exported files can be visualized in the ParaView.

In the Converge Line Plotting we can visualize our data in the form of graphs , same is included for different cases .

After Importing the files we get the mesh as :

Mesh Size for different Cases .

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

### As we reduce the size of the grid the number of cells also increase .

Velocity Counter and Diagram

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

Velocity Diagram:

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

### From the above graphs we can observe that as we make the grid lesser the better velocity profile is obtained and also at the walls the flow is resisted due to the effetct of shear and hence velocity at the middle area is maximum .

Pressure Counter

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

From Converge:

Total Cell Count :

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

### From the graph we can deduce that the number of cell requirement for a finer mesh is more .

Velocity Plot Inlet and Outlet :

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

### For finer mesh it takes a longer cycles to get the velocity stable or uniform .

Pressure plot at Inlet and Outlet :

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

### As expected the pressure is high at the start and the pressure reduces over the period of time as the flow gets stable .

Mass Flow Rate at Inlet and Outlet :

Case 1: dx = 2e-4m, dy = 2e-4m, dz = 2e-4m

Case 2: dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m

Case 3 dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m

### It can be clearly seen that the number of cycles required is more for the finer mesh . The mass remains the same at the end of simulation

Conclusion:

With the increase in grid size we reqire more cells counts , larger number of cycles & with more discritization we get more accurate results but the Computational time required is more .

Animation:

Find the Link below for the animation of Simulation Test in ParaView

• Simulation of Flow of Air in the Channel:https://www.youtube.com/watch?v=P3zFN3SlyaA
• Propogation of Air Velocity : https://www.youtube.com/watch?v=rVERK3gUPL0
• Variation in Pressure within the cahnnel : https://www.youtube.com/watch?v=KNfD-zc6N60